GENEVA — Cases of dementia — and the heavy social and financial burdens associated with them — are set to soar in the coming decades as life expectancy and medical care improve in poorer countries, the World Health Organization says.

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Some 35.6 million people were living with dementia in 2010, but that figure is set to double to 65.7 million by 2030, the U.N. health agency said Wednesday. In 2050, it expects the number of dementia cases to triple to 115.4 million.

Most dementia patients are cared for by relatives, who shoulder the bulk of the current estimated annual cost of $604 billion, WHO said.

In its first substantial report on the issue, the agency said the financial burden is expected to rise even faster than the number of cases.

Dementia, a brain illness that affects memory, behavior and the ability to perform even common tasks, affects mostly older people. About 70 percent of cases are believed to be caused by Alzheimer's.

In the last few decades dementia has become a major public health issue in rich countries. But with populations in poor and middle-income countries projected to grow and age rapidly over the coming decades, the agency appealed for greater public awareness and better support programs everywhere.

The share of cases in poor and middle-income countries is expected to rise from just under 60 percent today, to over 70 percent by 2050.

So far, only eight countries — including Britain, France and Japan — have national programs to address dementia, WHO said. Several others, such as the United States, have plans at the state level.

WHO said a lack of proper diagnosis is one of the obstacles to better dementia treatment. Even in rich countries more than half of dementia cases are overlooked until the disease has reached a late stage.

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